HDFS-4596. Shutting down namenode during checkpointing can lead to md5sum error. Contributed by Andrew Wang.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1456633 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-9407. Merge 1456704 from trunk

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Merge remote branch 'origin/branch-2' into branch-2-gd
Merge remote branch 'origin/branch-2-gd' into fb-YAHOO-270-branch-2-gd